As a result of increased demand for wireless devices with low duty cycles which transmit small amounts of data infrequently over large distances (e.g., smart sensors in remote locations), new efforts are emerging that attempt to develop standards for these devices based on existing wireless technologies and protocols. For example, the proposed IEEE 802.11ah specification specifies a wireless protocol for the sub 1 GHz frequency spectrum based on the 802.11 family of standards. The 802.11ah proposal will enable small battery powered wireless devices (e.g., sensors) to use Wi-Fi (IEEE 802.11) to connect to the Internet with very low power consumption. The 802.11ah proposal introduces a set of modulation and coding schemes (MCS0-8) with low data rates of between 0.8125 and 10.8375 Mbps. The 802.11ah standard also introduces a set of optional physical data rates lower then MCS0. These low data rate schemes of 0.203 Mbps and 0.406 Mbps extend transmission range by transmitting the packet multiple times sequentially using the lowest standard MCS (MCS0). The receiver may then combine the multiple copies of the packet to realize increased processing gains. While transmission range is increased, the rate is decreased (because of the need to transmit the packet multiple times—i.e. by transmitting the packet twice, the data rate is lowered from 0.8125 to 0.406 Mbps).
Each packet sent over a wireless network contains a preamble portion which allows another wireless device to recognize the packet and train its receiver to decode the packet. When the packet is duplicated for purposes of the lower physical rates, the preamble must also be duplicated so as to be detectable at the receiver. Thus some wireless protocols feature two different length preambles—a standard preamble and a long preamble for the low physical rates. Despite the fact that these lower physical rates are considered “optional,” because many wireless protocols (including 802.11) often utilize media access control (MAC) schemes such as carrier sense multiple access (CSMA) (in which a wireless device must sense that the channel is clear for a predefined time period prior to transmitting data over the medium), wireless devices must be able to recognize the longer preamble packets to determine if the channel is in use or not. As multiple preambles of disparate length are utilized, the receiver design complexity increases as the receiver must be trained to recognize additional preamble signatures. This in turn increases cost as additional circuitry will be required to detect the unique signature of each preamble length.